ABSTRACT

The prevalence of tobacco smoking and coffee drinking place nicotine and
caffeine among the most used licit drugs in many societies and their consumption
is often characterised by concurrent use. The pharmacological basis for any
putative interaction between these drugs remains unclear. Epidemiological
reports support anecdotal evidence, which suggests that smokers consume caffeine
to enhance the euphoric effects of nicotine. The aim of the present experiment
was to examine effects of chronic exposure to caffeine on responding maintained
by nicotine. Sprague-Dawley rats consuming caffeine (approximately 150-180 mg/kg
per day) in their drinking water for 7 days prior to the beginning and
throughout behavioural testing acquired intravenous nicotine self-administration
(0.03 mg/kg per infusion) more rapidly than did controls. In a cross-over
design, exclusion of caffeine brought levels of nicotine self-administration
back to baseline, while adding caffeine to the drinking water of control rats
increased responding maintained by nicotine over 90%. These findings strongly
suggest that caffeine can potentiate the reinforcing properties of nicotine,
thus highlighting the importance of environmental factors in shaping and
maintaining tobacco smoking.